Typically, doors are provided with a standard backset which defines the distance between the rotational axis of the operating knob and the edge of the door from which the latch bolt extends. Most modern doors are provided with a backset of 23/4" while older doors and a minority of modern doors have a backset of 23/8". Thus, if the door hardware needs to be replaced, the user must locate a door latch which has the identical backset. Accordingly, hardware suppliers must stock latches for both types of backsets.
Adjustable backset door latches have been developed which utilize various mechanisms to vary the distance between the door edge and the rotational axis of the latch knob. However, the available space within the door is limited and therefore the length of the latch must correspond to the door configuration. Several prior known latches with adjustable backsets employ telescopingly extendable mechanisms which require additional preparation of the door. Still other designs comprise complicated mechanisms which can not be cost-effectively manufactured or have an unacceptable failure rate.
Adjustable backset door latches including dead bolts are also known. Employment of deadlocking latches is useful for the purpose of reducing or deterring tampering with a lock mechanism so that the latch or lock mechanism once locked is not readily manipulated into an unlocked position by unauthorized persons. In dead locking mechanism the tendency has heretofore been to build a considerable ruggedness into the mechanism. Because of the growing tendency to reduce the size of casings and housings for cylinder lock sets and tubular lock sets, dead latch mechanisms which have been constructed in an attempt to emphasize security have been complicated to a considerable degree and have necessitated careful machining of close-fitting parts in order to make certain that the dead latch mechanism operates with the consistency and security expected. The designs and constructions thus employed heretofore have invariably resulted in an expensive construction which has made the retail price of lock hardware of this type very expensive.